Field of the Invention
The present invention relates to a shift controlling method for an automatic transmission and a system therefor.
In an automatic transmission which can establish a plurality of gear ratios by selectively supply hydraulic pressure to a plurality of friction engagement elements, there has been known the automatic transmission, in which either an automatic shifting mode to automatically establish a predetermined gear ratio from a preliminarily set map of shifting range on the basis of a vehicle driving condition, such as an engine load represented by a throttle opening, and a vehicle speed, or a manual shifting mode, in which the driver establishes a desired gear ratio by manual operation, can be selected.
In order to prevent shift shock from increasing due to fluctuation of shifting performance of respective individual automatic transmissions due to tolerance in spool valves, springs and so on, for selectively supplying a hydraulic pressure to the friction engagement elements, or secular change of the friction engagement elements, Japanese Patent Application Laid-open No. 63-92863 (1988) and Japanese Patent Application Laid-open No. 1-169164 (1989) disclose system which performs learning control so that an actual shifting period converges to a targeted shifting period to from initiation of shifting to completion of shifting. In the learning control of the shifting period, the target sifting period and the actual shifting period are compared to correct a hydraulic pressure value preliminarily stored in a map or the like to output the corrected hydraulic pressure upon next shifting so as to converge the actual shifting period to the target shifting period.
When the learning control of the shifting period is performed in the automatic shifting mode, since the vehicle driving conditions to cause shifting operation are determined univocally, required storage capacity of RAM to be used for storing the content of learning is relatively small. However, when learning control of the shifting period is attempted during manual shifting mode, huge amount of storage capacity is required for RAM to be used since shifting operation tends to be performed in arbitrary vehicle driving condition and all vehicle driving conditions where the manual shifting operation is taken place. Furthermore, control logic becomes too complicate.
In order to avoid such problem, in the conventional shift control system for an automatic transmission, as disclosed in Japanese Patent Application Laid-open No. 5-332437 (1993), learning control of the shifting period is inhibited while manual shifting mode is selected to simplify control logic to permit use of RAM having small storage capacity.
In case of the conventional shift control system of the automatic transmission disclosed in Japanese Patent Application Laid-open No. 5-332437, if automatic shifting mode is rarely selected and manual shifting mode is continuously used for a long period, learning control of the shifting period is substantially not performed. As a result, it becomes impossible to prevent increasing of shift shock or degradation of durability of the frictional engaging elements.
The foregoing problem will not be happened when a proportion of driving of the vehicle in the automatic shifting mode is sufficiently large and when manual shifting mode is selected for a short period.